The temperature dependence of biochemical and chemical reaction rates poses a particular challenge to efforts to improve reaction efficiency and speed by miniaturization. A time-domain approach, whereby not only the reaction volume but also the entire housing is kept at a desired temperature, is only suitable for isothermal conditions. If temperature needs to be changed or cycled in a rapid and controlled manner, the added thermal mass of the housing limits the rate and/or precision that can be achieved.
In the space-domain approach (see, e.g., Kopp, et al., Science 1998, 280, 1046-1048; Burns, et al., Science 1998, 282, 484-487; Chiou et al., Anal. Chem. 2001, 73, 2018-2021; and Nakano et al., Biosci. Biotechnol. Biochem. 1994, 58, 349-352), different parts of the reaction housing are kept at different temperatures, and reaction volume is brought in thermal contact with a desired part of the housing to keep it at the temperature of that part. If necessary, the reaction volume can then be moved to a different part of the housing to change the temperature; and, depending on the trajectory of the reaction volume, the temperature profile of it can be adjusted or cycled as desired. In the art, most of the implementations of the space-domain dynamic thermal control have been directed to miniaturized PCR thermocycling. Continuous meandering or spiral channels laid across temperature zones have been demonstrated for continuous flowthrough amplification (see, e.g., Fukuba et al., CHEMICAL ENGINEERING JOURNAL 101 (1-3): 151-156 Aug. 1, 2004); direct-path arrangements with a reaction slug moving back and forth have been described (see, e.g., Chiou et al., Anal. Chem. 2001, 73, 2018-2021); and finally, cycling of an individual reaction through a loop has been demonstrated (see, e.g., Jian Liu Markus Enzelberger et al. Electrophoresis 2002, 23, 1531-1536).